Yes I know its not being developed anymore - much to my disappointment - but Google Wave could prove a useful way to run a Play By Mail (PBM) game with the all the functionality of emails, with graphics and attachments, but with the added advantage of realtime information, with an easier way for all parties involved to interact at the same time. Also without the hassle of using IM. One could also have split off waves between players, and between GM and players, while maintaining a main game feed.
There are some cool possibilities there, and until they re-develop the tool into something else, it will still be available to use.
More to come...